JP2007-240496 A, published by the Japan Patent Office in 2007, proposes a non-contact type torque sensor that detects a steering wheel operation torque that is input into a vehicle power steering device by a driver of a vehicle. Upon sensing the steering wheel operation torque, the power steering device supplements an assisting force of an electric motor to the steering wheel operation torque, thereby accomplishing steering of the vehicle with an input of a small steering wheel operation toque.
The torque sensor comprises a magnetic force generation part which rotates together with an end of a torsion bar in a housing. a rotating magnetic circuit that rotates together with another end of the torsion bar, a stationary magnetic circuit fixed to a housing, and a magnetic force sensing element that detects a density of magnetic flux led to the stationary magnetic circuit.
When the torsion bar undertakes a torsional deformation in response to an input torque, the relative rotation positions of the magnetic force generation part and the rotating magnetic circuit vary As result, a density of the magnetic flux that is led from the magnetic force generation part to the stationary magnetic circuit via the rotating magnetic circuit varies and the magnetic force sensing element outputs a signal indicative of the variation in the magnetic flux.
Further, certain electric power steering devices comprise a rotation position sensor that detects a steering angle of steered wheels of the vehicle from a rotation position of the electric motor, and a position sensor that detects a neutral position of the steering wheel of the vehicle so as to cause a zero point for the measurement of the steering angle to coincide with the neutral position of the steering wheel.